·There are some limitations of compile time array. E.g. If we want to
change the value of an array element, we need to make changes in the program
source code where the array’s element is defined and then recompile the
program.

·In pre-runtime array, we maintain the array element in separate file.
Hence, if we are making any change in array element we can just change this
file containing the array element; we don’t need to compile the source program
again and again as in compile time array.

·The file that stores the array element must be defined in the F specs
with ‘T’ as File Designation entry.

·Record length is also a mandatory entry in F spec.

length of record = Perrcd *size of 1 element

·The file is opened at program initialization. At that time the array
loads from this external file.

·To define the array in our program, we use keyword FROMFILE() instead of
CTDATA().